The present invention relates generally to industrial curtains used as environmental closures for openings through which traffic can still pass. The curtains generally comprise a plurality of strips suspended contiguously to each other from a hanger fixed adjacent to a top margin of the opening, each strip consisting essentially of a length of flexible material terminating adjacent to a lower margin of the opening. The present invention relates particularly to an improved configuration for the material forming the strips of such industrial curtains so that vision through the curtain is improved.
Goods are often required to be transported from one area of a manufacturing or storage facility to another where one or the other of the areas is heated, air-conditioned or even refrigerated. Sometime other environmental concerns need to be addressed such as dust, fumes, smoke, dirt, or even noise. Where the traffic is only occasional, conventional doors can be employed to close any doorway between the two areas. Where the traffic is considerable, the use of conventional doors gives way to suspended flexible screens or curtains that inhibit the wholesale transfer of heated or cooled air from one area to the other yet still permit goods-transporting vehicles to pass through with little effort. Early screens were sometimes made of rubber as shown, for example, in U.S. Pat. No. 2,122,532. For safety reasons, it is desirable that the curtain be sufficiently transparent that one operating a transporting vehicle be able to see any hazard or obstruction that might exist on an opposite side of a screen before proceeding through. Persons on the opposite side of a screen also desire to be able to see oncoming transport vehicles so appropriate evasive action can be taken. Thus, plastic materials, which were more or less transparent, such as polyvinyl chloride and polyethylene, were adopted as the preferred materials for forming such screens as shown, for example, in U.S. Pat. Nos. 4,095,642, 4,165,778, 4,232,725, 4,367,781, and 4,607,678.
Plastics such as polyethylene and polyvinyl chloride have two characteristics that have been recognized as detrimental to completely satisfactory performance in industrial doorway curtains. First, the plastic strips are often electro-statically attracted to each other so that they resist separation from each other as the goods and transporting vehicles attempt to pass through the curtain. This problem is particularly evident with the curtain is initially installed. Second, the plastics are generally much softer than the edges and corners of the transporting vehicles and goods packages that pass through the curtains. Thus, the curtain strips quickly become scuffed and scratched by the passing traffic to the point that the originally transparent strips become effectively opaque. In attempting to solve both of these and other related problems special overlapping attachments have been added to the strips, the edges of the strips have included bulbous enlargements, and ridges have been added to the body of the strips as shown, for example, in U.S. Pat. Nos. 4,086,950 and 4,289,190. Despite these attempts to solve the problems of electrostatic attraction and visibility, the problems remain.
The present invention attempts to directly address the problem of preventing scuffing and scratching of the strips of plastic forming the curtain thus ensuring substantially transparency of the strips and ensuring that vision through the strip is unimpeded while at the same time forming a curtain of minimal cost.
A material for use in an industrial traffic curtain in accordance with the present invention consists essentially of a length, as needed, of a flexible transparent material, such as polyvinyl chloride, having a substantially uniform longitudinal cross-section, which can be achieved by way of a conventional extrusion process. The strip of material has a transverse cross-section defined by first and second parallel surfaces defining a web of the curtain, the surfaces having an array of regularly spaced, generally rectangular longitudinal ribs of predetermined height and width. The ribs on the first surface are arranged to be coincident with the ribs on the second surface. In one embodiment, each adjacent pair of ribs on each of the surfaces is interspersed by a linear bead having a height dimension approximating the height dimension of the adjacent pair of ribs. The linear beads have a width dimension less than about 10% of the distance between the adjacent pair of ribs so that the space between each pair of ribs remains substantially transparent and vision through the strip is unimpeded. In another embodiment the intermediate linear beads are formed to have substantially the same shape and dimension as the ribs, so that a greater portion of the mass of the curtain is provided in the ribs than in the web forming the essentially transparent portion of the curtain material.
Generally, the thickness of the plastic forming the web of the curtain, measured between the first and second surfaces, is between about 0.020 in. and 0.080 in. This web thickness is generally thinner than most conventional industrial traffic curtain materials, which contributes to a lower cost for the present product. There is a practical lower limit on the thickness of such curtain materials, as a material that is too thin will be easily disturbed by air currents, which is inconsistent with the purpose of such curtain materials to constitute environmental barriers. The height of the ribs, on the other hand, is generally proportionately greater than conventional industrial traffic curtain materials, which provides the necessary resistance to air currents, thus allowing the thinning of the web portion which again contributes to a lower cost for the present product.
The ribs are also spaced apart by a distance that is only about xc2xc to xc2xd the usual spacing. This narrower rib spacing has the tendency to protect the intervening surfaces of the curtain from abrasion far better than conventional industrial curtain materials. The closer spacing has the added advantage of causing less cuts and other injuries to persons passing thorough the curtain. The narrower spacing coupled with the opposed positioning of the ribs provides advantages both in the manufacturing process and in use. In the manufacturing process, the opposed positioning of the ribs provides a better coiling surface for better handling of the curtain material. The opposed positioning and narrow spacing improves the thermal insulating function of the curtain by trapping more air in the pockets created between the ribs.
In one embodiment, linear beads are positioned about midway between the more narrowly spaced ribs. The height of the outermost surface of the linear beads above the supporting surface is generally between about 60% and 80% of the height of the rectangular ribs. The linear beads aid in preventing abrasion of the surface of the web material by passing machinery in a manner similar to the ribs. The width of the linear beads is generally between only about 5% and 15% of the distance between adjacent ribs. This width for the intervening beads is much smaller than any ribs previously employed, which has the advantage of presenting such a small line disturbance on the web surface that the presence of the linear bead does not significantly detract from the visibility through the web during use. The cross-sectional shape of the linear bead can be essentially semicircular or triangular to best protect the screen surface from abrasion.
Unlike prior plastic strip doors, such as are shown in U.S. Pat. Nos. 4,086,950 and 4,289,190, each strip is provided with a regularly spaced coincident series of ribs on both sides of each strip, the ribs having sufficient width to allow the overlapping strips forming the curtain to be positioned so that the outer surfaces of the ribs are confronting and contacting each other when the curtain is undisturbed. The spaces defined between the ribs form insulating pockets that improve the environmental barrier performance of the curtain, without reducing visibility through curtain. The closely spaced ribs act to protect the web surfaces between the ribs, while the narrow contact area of the confronting rib surfaces diminishes any electrostatic attraction between the curtain strips.
Other features and advantages of the present invention will become apparent to those skilled in the art upon considering the following description of the preferred embodiments of the present invention, which makes reference to the accompanying drawings.